To study a variety of inter-related problems at both the clinical and experimental level involving the basic physiology and pharmacology of iodinated contrast agents. Separate projects include: 1) analysis of the acute renal response to the iothalamatedimer in the dog; (a) evaluation of acute changes in GFR during intravenous urography in man; (b) determination of late urinary concentration of urographic agents in man, particularly in patients with disorders characterized by oliquria or dehydratior; 3) prospective analysis of the incidence of mild and/or slight renal dysfunction following cholecystography in man; 4) determine whether cholecystographic agents are active in inducing enzymes related to drug metabolism or excretion; 5) characterize the nature of the choleresis induced by iodipamide to determine whether this is simply related to solute excretion alone or to a specific effect on the biliary tract transport of electrolyte; and 6) evaluate the role of intracellular hepatic proteins in hepatic secretory transport utilzing cinchophen augmentation of iophenoxate secretion as an experimental probe.